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 $113.41   6.870%   $121.2013   $121.20   $121.20   $121.20  
  Purchase #2 $250.68   11.340%   $279.1071   $279.11   $279.10   $279.10  
  Purchase #3 $200.66   11.359%   $223.453   $223.45   $223.45   $223.50  
  Purchase #4 $62.86   6.342%   $66.8466   $66.85   $66.85   $66.80  
  Purchase #5 $206.56   4.829%   $216.5348   $216.53   $216.55   $216.50  
  Purchase #6 $118.64   11.336%   $132.089   $132.09   $132.10   $132.10  
  Purchase #7 $68.94   7.498%   $74.1091   $74.11   $74.10   $74.10  
  7 purchase totals = $1,021.75       $1,113.3409   $1,113.34   $1,113.35   $1,113.30