Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.96   5.693%   $251.5071   $251.51   $251.50   $251.50  
  Purchase #2 $198.80   3.547%   $205.8514   $205.85   $205.85   $205.90  
  Purchase #3 $202.39   11.250%   $225.1589   $225.16   $225.15   $225.20  
  Purchase #4 $167.92   11.774%   $187.6909   $187.69   $187.70   $187.70  
  Purchase #5 $141.84   12.741%   $159.9118   $159.91   $159.90   $159.90  
  Purchase #6 $200.82   5.642%   $212.1503   $212.15   $212.15   $212.20  
  Purchase #7 $156.40   4.488%   $163.4192   $163.42   $163.40   $163.40  
  7 purchase totals = $1,306.13       $1,405.6896   $1,405.69   $1,405.65   $1,405.80