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 $205.70   13.126%   $232.7002   $232.70   $232.70   $232.70  
  Purchase #2 $232.31   8.438%   $251.9123   $251.91   $251.90   $251.90  
  Purchase #3 $172.83   4.219%   $180.1217   $180.12   $180.10   $180.10  
  Purchase #4 $162.43   3.769%   $168.552   $168.55   $168.55   $168.60  
  Purchase #5 $67.73   12.550%   $76.2301   $76.23   $76.25   $76.20  
  Purchase #6 $124.85   11.356%   $139.028   $139.03   $139.05   $139.00  
  Purchase #7 $172.59   6.776%   $184.2847   $184.28   $184.30   $184.30  
  7 purchase totals = $1,138.44       $1,232.8290   $1,232.82   $1,232.85   $1,232.80