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 $85.62   13.801%   $97.4364   $97.44   $97.45   $97.40  
  Purchase #2 $153.39   10.794%   $169.9469   $169.95   $169.95   $169.90  
  Purchase #3 $127.62   3.237%   $131.7511   $131.75   $131.75   $131.80  
  Purchase #4 $87.98   11.759%   $98.3256   $98.33   $98.35   $98.30  
  Purchase #5 $220.71   12.209%   $247.6565   $247.66   $247.65   $247.70  
  Purchase #6 $158.89   3.398%   $164.2891   $164.29   $164.30   $164.30  
  Purchase #7 $223.94   5.855%   $237.0517   $237.05   $237.05   $237.10  
  7 purchase totals = $1,058.15       $1,146.4573   $1,146.47   $1,146.50   $1,146.50