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 $84.51   11.552%   $94.2726   $94.27   $94.25   $94.30  
  Purchase #2 $150.97   7.297%   $161.9863   $161.99   $162.00   $162.00  
  Purchase #3 $152.36   10.779%   $168.7829   $168.78   $168.80   $168.80  
  Purchase #4 $25.91   11.325%   $28.8443   $28.84   $28.85   $28.80  
  Purchase #5 $102.78   5.367%   $108.2962   $108.30   $108.30   $108.30  
  Purchase #6 $67.30   11.157%   $74.8087   $74.81   $74.80   $74.80  
  Purchase #7 $171.75   10.219%   $189.3011   $189.30   $189.30   $189.30  
  7 purchase totals = $755.58       $826.2921   $826.29   $826.30   $826.30