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 $94.38   3.770%   $97.9381   $97.94   $97.95   $97.90  
  Purchase #2 $158.61   3.384%   $163.9774   $163.98   $164.00   $164.00  
  Purchase #3 $5.36   11.136%   $5.9569   $5.96   $5.95   $6.00  
  Purchase #4 $91.79   13.818%   $104.4735   $104.47   $104.45   $104.50  
  Purchase #5 $47.69   6.553%   $50.8151   $50.82   $50.80   $50.80  
  Purchase #6 $193.64   5.586%   $204.4567   $204.46   $204.45   $204.50  
  Purchase #7 $72.68   4.500%   $75.9506   $75.95   $75.95   $76.00  
  7 purchase totals = $664.15       $703.5683   $703.58   $703.55   $703.70