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 $112.40   3.779%   $116.6476   $116.65   $116.65   $116.60  
  Purchase #2 $230.57   13.444%   $261.5678   $261.57   $261.55   $261.60  
  Purchase #3 $122.56   3.524%   $126.879   $126.88   $126.90   $126.90  
  Purchase #4 $155.43   6.317%   $165.2485   $165.25   $165.25   $165.20  
  Purchase #5 $111.94   8.586%   $121.5512   $121.55   $121.55   $121.60  
  Purchase #6 $187.72   6.289%   $199.5257   $199.53   $199.55   $199.50  
  Purchase #7 $225.86   13.273%   $255.8384   $255.84   $255.85   $255.80  
  7 purchase totals = $1,146.48       $1,247.2582   $1,247.27   $1,247.30   $1,247.20