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 $53.68   12.111%   $60.1812   $60.18   $60.20   $60.20  
  Purchase #2 $33.96   6.121%   $36.0387   $36.04   $36.05   $36.00  
  Purchase #3 $228.84   9.724%   $251.0924   $251.09   $251.10   $251.10  
  Purchase #4 $177.98   10.399%   $196.4881   $196.49   $196.50   $196.50  
  Purchase #5 $216.40   9.316%   $236.5598   $236.56   $236.55   $236.60  
  Purchase #6 $117.38   6.641%   $125.1752   $125.18   $125.20   $125.20  
  Purchase #7 $58.30   7.810%   $62.8532   $62.85   $62.85   $62.90  
  7 purchase totals = $886.54       $968.3886   $968.39   $968.45   $968.50