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 $96.47   3.152%   $99.5107   $99.51   $99.50   $99.50  
  Purchase #2 $126.59   4.502%   $132.2891   $132.29   $132.30   $132.30  
  Purchase #3 $248.91   9.486%   $272.5216   $272.52   $272.50   $272.50  
  Purchase #4 $231.99   4.234%   $241.8125   $241.81   $241.80   $241.80  
  Purchase #5 $208.51   8.743%   $226.74   $226.74   $226.75   $226.70  
  Purchase #6 $66.29   10.804%   $73.452   $73.45   $73.45   $73.50  
  Purchase #7 $140.55   11.654%   $156.9297   $156.93   $156.95   $156.90  
  7 purchase totals = $1,119.31       $1,203.2556   $1,203.25   $1,203.25   $1,203.20