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 $143.77   3.600%   $148.9457   $148.95   $148.95   $148.90  
  Purchase #2 $18.77   6.531%   $19.9959   $20.00   $20.00   $20.00  
  Purchase #3 $139.59   6.777%   $149.05   $149.05   $149.05   $149.10  
  Purchase #4 $107.59   3.165%   $110.9952   $111.00   $111.00   $111.00  
  Purchase #5 $140.76   7.204%   $150.9004   $150.90   $150.90   $150.90  
  Purchase #6 $121.74   11.492%   $135.7304   $135.73   $135.75   $135.70  
  Purchase #7 $187.62   10.389%   $207.1118   $207.11   $207.10   $207.10  
  7 purchase totals = $859.84       $922.7294   $922.74   $922.75   $922.70