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 $74.46   8.714%   $80.9484   $80.95   $80.95   $80.90  
  Purchase #2 $146.69   6.733%   $156.5666   $156.57   $156.55   $156.60  
  Purchase #3 $220.53   5.849%   $233.4288   $233.43   $233.45   $233.40  
  Purchase #4 $33.47   6.551%   $35.6626   $35.66   $35.65   $35.70  
  Purchase #5 $245.31   11.287%   $272.9981   $273.00   $273.00   $273.00  
  Purchase #6 $64.84   11.620%   $72.3744   $72.37   $72.35   $72.40  
  Purchase #7 $180.61   8.170%   $195.3658   $195.37   $195.35   $195.40  
  7 purchase totals = $965.91       $1,047.3447   $1,047.35   $1,047.30   $1,047.40