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 $89.95   9.234%   $98.256   $98.26   $98.25   $98.30  
  Purchase #2 $9.41   12.334%   $10.5706   $10.57   $10.55   $10.60  
  Purchase #3 $92.68   4.276%   $96.643   $96.64   $96.65   $96.60  
  Purchase #4 $249.48   4.357%   $260.3498   $260.35   $260.35   $260.30  
  Purchase #5 $201.48   13.717%   $229.117   $229.12   $229.10   $229.10  
  Purchase #6 $89.35   9.394%   $97.7435   $97.74   $97.75   $97.70  
  Purchase #7 $217.67   12.555%   $244.9985   $245.00   $245.00   $245.00  
  7 purchase totals = $950.02       $1,037.6784   $1,037.68   $1,037.65   $1,037.60