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 $20.32   7.433%   $21.8304   $21.83   $21.85   $21.80  
  Purchase #2 $80.34   4.727%   $84.1377   $84.14   $84.15   $84.10  
  Purchase #3 $64.92   4.845%   $68.0654   $68.07   $68.05   $68.10  
  Purchase #4 $41.32   6.651%   $44.0682   $44.07   $44.05   $44.10  
  Purchase #5 $150.84   5.552%   $159.2146   $159.21   $159.20   $159.20  
  Purchase #6 $32.53   13.360%   $36.876   $36.88   $36.90   $36.90  
  Purchase #7 $136.79   13.811%   $155.6821   $155.68   $155.70   $155.70  
  7 purchase totals = $527.06       $569.8744   $569.88   $569.90   $569.90