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 $88.57   4.719%   $92.7496   $92.75   $92.75   $92.70  
  Purchase #2 $95.65   11.401%   $106.5551   $106.56   $106.55   $106.60  
  Purchase #3 $8.30   12.582%   $9.3443   $9.34   $9.35   $9.30  
  Purchase #4 $76.41   4.730%   $80.0242   $80.02   $80.00   $80.00  
  Purchase #5 $47.44   12.528%   $53.3833   $53.38   $53.40   $53.40  
  Purchase #6 $81.29   7.130%   $87.086   $87.09   $87.10   $87.10  
  Purchase #7 $237.25   5.267%   $249.746   $249.75   $249.75   $249.70  
  7 purchase totals = $634.91       $678.8885   $678.89   $678.90   $678.80