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 $53.35   6.715%   $56.9325   $56.93   $56.95   $56.90  
  Purchase #2 $236.98   13.160%   $268.1666   $268.17   $268.15   $268.20  
  Purchase #3 $77.59   6.596%   $82.7078   $82.71   $82.70   $82.70  
  Purchase #4 $130.97   6.851%   $139.9428   $139.94   $139.95   $139.90  
  Purchase #5 $240.53   3.582%   $249.1458   $249.15   $249.15   $249.10  
  Purchase #6 $50.64   7.768%   $54.5737   $54.57   $54.55   $54.60  
  Purchase #7 $166.90   6.237%   $177.3096   $177.31   $177.30   $177.30  
  7 purchase totals = $956.96       $1,028.7788   $1,028.78   $1,028.75   $1,028.70