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 $95.75   9.362%   $104.7141   $104.71   $104.70   $104.70  
  Purchase #2 $20.75   6.644%   $22.1286   $22.13   $22.15   $22.10  
  Purchase #3 $98.66   5.263%   $103.8525   $103.85   $103.85   $103.90  
  Purchase #4 $57.82   7.836%   $62.3508   $62.35   $62.35   $62.40  
  Purchase #5 $59.88   10.163%   $65.9656   $65.97   $65.95   $66.00  
  Purchase #6 $47.74   10.319%   $52.6663   $52.67   $52.65   $52.70  
  Purchase #7 $124.73   5.788%   $131.9494   $131.95   $131.95   $131.90  
  7 purchase totals = $505.33       $543.6273   $543.63   $543.60   $543.70