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 $209.70   6.354%   $223.0243   $223.02   $223.00   $223.00  
  Purchase #2 $114.97   3.767%   $119.3009   $119.30   $119.30   $119.30  
  Purchase #3 $148.82   5.108%   $156.4217   $156.42   $156.40   $156.40  
  Purchase #4 $196.37   5.187%   $206.5557   $206.56   $206.55   $206.60  
  Purchase #5 $31.95   4.766%   $33.4727   $33.47   $33.45   $33.50  
  Purchase #6 $227.96   11.522%   $254.2256   $254.23   $254.25   $254.20  
  Purchase #7 $27.40   6.757%   $29.2514   $29.25   $29.25   $29.30  
  7 purchase totals = $957.17       $1,022.2523   $1,022.25   $1,022.20   $1,022.30