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 $110.65   13.452%   $125.5346   $125.53   $125.55   $125.50  
  Purchase #2 $162.42   11.330%   $180.8222   $180.82   $180.80   $180.80  
  Purchase #3 $58.56   9.827%   $64.3147   $64.31   $64.30   $64.30  
  Purchase #4 $64.46   12.523%   $72.5323   $72.53   $72.55   $72.50  
  Purchase #5 $61.64   11.389%   $68.6602   $68.66   $68.65   $68.70  
  Purchase #6 $241.39   11.794%   $269.8595   $269.86   $269.85   $269.90  
  Purchase #7 $248.50   5.109%   $261.1959   $261.20   $261.20   $261.20  
  7 purchase totals = $947.62       $1,042.9194   $1,042.91   $1,042.90   $1,042.90