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 $87.39   6.793%   $93.3264   $93.33   $93.35   $93.30  
  Purchase #2 $201.92   11.733%   $225.6113   $225.61   $225.60   $225.60  
  Purchase #3 $177.85   7.292%   $190.8188   $190.82   $190.80   $190.80  
  Purchase #4 $131.51   3.648%   $136.3075   $136.31   $136.30   $136.30  
  Purchase #5 $67.53   12.339%   $75.8625   $75.86   $75.85   $75.90  
  Purchase #6 $87.92   8.672%   $95.5444   $95.54   $95.55   $95.50  
  Purchase #7 $234.54   6.739%   $250.3457   $250.35   $250.35   $250.30  
  7 purchase totals = $988.66       $1,067.8166   $1,067.82   $1,067.80   $1,067.70