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 $22.47   13.541%   $25.5127   $25.51   $25.50   $25.50  
  Purchase #2 $242.67   7.445%   $260.7368   $260.74   $260.75   $260.70  
  Purchase #3 $106.66   11.194%   $118.5995   $118.60   $118.60   $118.60  
  Purchase #4 $56.60   5.319%   $59.6106   $59.61   $59.60   $59.60  
  Purchase #5 $154.62   10.448%   $170.7747   $170.77   $170.75   $170.80  
  Purchase #6 $247.91   10.400%   $273.6926   $273.69   $273.70   $273.70  
  Purchase #7 $94.75   8.540%   $102.8417   $102.84   $102.85   $102.80  
  7 purchase totals = $925.68       $1,011.7686   $1,011.76   $1,011.75   $1,011.70