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 $249.34   10.808%   $276.2887   $276.29   $276.30   $276.30  
  Purchase #2 $18.34   3.687%   $19.0162   $19.02   $19.00   $19.00  
  Purchase #3 $90.37   5.738%   $95.5554   $95.56   $95.55   $95.60  
  Purchase #4 $121.27   7.751%   $130.6696   $130.67   $130.65   $130.70  
  Purchase #5 $199.55   13.786%   $227.06   $227.06   $227.05   $227.10  
  Purchase #6 $146.90   10.254%   $161.9631   $161.96   $161.95   $162.00  
  Purchase #7 $118.87   11.533%   $132.5793   $132.58   $132.60   $132.60  
  7 purchase totals = $944.64       $1,043.1323   $1,043.14   $1,043.10   $1,043.30