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 $140.84   6.516%   $150.0171   $150.02   $150.00   $150.00  
  Purchase #2 $19.58   12.528%   $22.033   $22.03   $22.05   $22.00  
  Purchase #3 $12.94   6.226%   $13.7456   $13.75   $13.75   $13.70  
  Purchase #4 $28.85   11.140%   $32.0639   $32.06   $32.05   $32.10  
  Purchase #5 $59.52   8.811%   $64.7643   $64.76   $64.75   $64.80  
  Purchase #6 $244.84   9.439%   $267.9504   $267.95   $267.95   $268.00  
  Purchase #7 $199.48   3.413%   $206.2883   $206.29   $206.30   $206.30  
  7 purchase totals = $706.05       $756.8626   $756.86   $756.85   $756.90