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 $87.92   10.477%   $97.1314   $97.13   $97.15   $97.10  
  Purchase #2 $197.57   6.697%   $210.8013   $210.80   $210.80   $210.80  
  Purchase #3 $107.43   9.400%   $117.5284   $117.53   $117.55   $117.50  
  Purchase #4 $236.29   13.136%   $267.3291   $267.33   $267.35   $267.30  
  Purchase #5 $55.69   9.202%   $60.8146   $60.81   $60.80   $60.80  
  Purchase #6 $33.86   7.697%   $36.4662   $36.47   $36.45   $36.50  
  Purchase #7 $73.27   4.611%   $76.6485   $76.65   $76.65   $76.60  
  7 purchase totals = $792.03       $866.7195   $866.72   $866.75   $866.60