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 $67.66   10.285%   $74.6188   $74.62   $74.60   $74.60  
  Purchase #2 $94.38   5.523%   $99.5926   $99.59   $99.60   $99.60  
  Purchase #3 $158.80   3.702%   $164.6788   $164.68   $164.70   $164.70  
  Purchase #4 $92.72   8.535%   $100.6337   $100.63   $100.65   $100.60  
  Purchase #5 $118.28   3.785%   $122.7569   $122.76   $122.75   $122.80  
  Purchase #6 $186.52   11.219%   $207.4457   $207.45   $207.45   $207.40  
  Purchase #7 $59.67   3.173%   $61.5633   $61.56   $61.55   $61.60  
  7 purchase totals = $778.03       $831.2898   $831.29   $831.30   $831.30