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 $24.74   4.317%   $25.808   $25.81   $25.80   $25.80  
  Purchase #2 $229.75   11.366%   $255.8634   $255.86   $255.85   $255.90  
  Purchase #3 $134.89   10.610%   $149.2018   $149.20   $149.20   $149.20  
  Purchase #4 $109.75   9.107%   $119.7449   $119.74   $119.75   $119.70  
  Purchase #5 $182.76   10.794%   $202.4871   $202.49   $202.50   $202.50  
  Purchase #6 $66.30   11.534%   $73.947   $73.95   $73.95   $73.90  
  Purchase #7 $168.83   13.367%   $191.3975   $191.40   $191.40   $191.40  
  7 purchase totals = $917.02       $1,018.4497   $1,018.45   $1,018.45   $1,018.40