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 $178.77   13.556%   $203.0041   $203.00   $203.00   $203.00  
  Purchase #2 $25.47   4.165%   $26.5308   $26.53   $26.55   $26.50  
  Purchase #3 $199.63   8.774%   $217.1455   $217.15   $217.15   $217.10  
  Purchase #4 $195.27   7.257%   $209.4407   $209.44   $209.45   $209.40  
  Purchase #5 $97.76   11.132%   $108.6426   $108.64   $108.65   $108.60  
  Purchase #6 $113.30   13.732%   $128.8584   $128.86   $128.85   $128.90  
  Purchase #7 $46.98   7.701%   $50.5979   $50.60   $50.60   $50.60  
  7 purchase totals = $857.18       $944.2200   $944.22   $944.25   $944.10