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 $244.86   3.447%   $253.3003   $253.30   $253.30   $253.30  
  Purchase #2 $216.99   8.751%   $235.9788   $235.98   $236.00   $236.00  
  Purchase #3 $54.92   11.338%   $61.1468   $61.15   $61.15   $61.10  
  Purchase #4 $111.85   7.839%   $120.6179   $120.62   $120.60   $120.60  
  Purchase #5 $244.27   5.762%   $258.3448   $258.34   $258.35   $258.30  
  Purchase #6 $30.96   9.382%   $33.8647   $33.86   $33.85   $33.90  
  Purchase #7 $53.54   10.129%   $58.9631   $58.96   $58.95   $59.00  
  7 purchase totals = $957.39       $1,022.2164   $1,022.21   $1,022.20   $1,022.20