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 $178.90   4.507%   $186.963   $186.96   $186.95   $187.00  
  Purchase #2 $62.80   11.380%   $69.9466   $69.95   $69.95   $69.90  
  Purchase #3 $160.89   7.769%   $173.3895   $173.39   $173.40   $173.40  
  Purchase #4 $41.49   3.742%   $43.0426   $43.04   $43.05   $43.00  
  Purchase #5 $87.45   7.382%   $93.9056   $93.91   $93.90   $93.90  
  Purchase #6 $109.36   12.157%   $122.6549   $122.65   $122.65   $122.70  
  Purchase #7 $195.84   7.541%   $210.6083   $210.61   $210.60   $210.60  
  7 purchase totals = $836.73       $900.5105   $900.51   $900.50   $900.50