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 $181.50   11.793%   $202.9043   $202.90   $202.90   $202.90  
  Purchase #2 $58.80   12.765%   $66.3058   $66.31   $66.30   $66.30  
  Purchase #3 $78.90   11.432%   $87.9198   $87.92   $87.90   $87.90  
  Purchase #4 $95.61   8.804%   $104.0275   $104.03   $104.05   $104.00  
  Purchase #5 $48.27   4.333%   $50.3615   $50.36   $50.35   $50.40  
  Purchase #6 $173.95   5.220%   $183.0302   $183.03   $183.05   $183.00  
  Purchase #7 $62.84   10.440%   $69.4005   $69.40   $69.40   $69.40  
  7 purchase totals = $699.87       $763.9496   $763.95   $763.95   $763.90