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 $105.94   5.118%   $111.362   $111.36   $111.35   $111.40  
  Purchase #2 $54.79   3.419%   $56.6633   $56.66   $56.65   $56.70  
  Purchase #3 $22.53   13.363%   $25.5407   $25.54   $25.55   $25.50  
  Purchase #4 $248.93   5.443%   $262.4793   $262.48   $262.50   $262.50  
  Purchase #5 $107.65   10.398%   $118.8434   $118.84   $118.85   $118.80  
  Purchase #6 $117.48   6.434%   $125.0387   $125.04   $125.05   $125.00  
  Purchase #7 $101.86   13.184%   $115.2892   $115.29   $115.30   $115.30  
  7 purchase totals = $759.18       $815.2166   $815.21   $815.25   $815.20