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 $59.92   13.362%   $67.9265   $67.93   $67.95   $67.90  
  Purchase #2 $191.94   9.304%   $209.7981   $209.80   $209.80   $209.80  
  Purchase #3 $122.46   10.314%   $135.0905   $135.09   $135.10   $135.10  
  Purchase #4 $158.65   4.264%   $165.4148   $165.41   $165.40   $165.40  
  Purchase #5 $44.97   12.708%   $50.6848   $50.68   $50.70   $50.70  
  Purchase #6 $90.54   6.836%   $96.7293   $96.73   $96.75   $96.70  
  Purchase #7 $9.88   11.370%   $11.0034   $11.00   $11.00   $11.00  
  7 purchase totals = $678.36       $736.6474   $736.64   $736.70   $736.60