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 $226.81   4.593%   $237.2274   $237.23   $237.25   $237.20  
  Purchase #2 $177.42   13.638%   $201.6165   $201.62   $201.60   $201.60  
  Purchase #3 $134.36   8.437%   $145.696   $145.70   $145.70   $145.70  
  Purchase #4 $115.48   11.138%   $128.3422   $128.34   $128.35   $128.30  
  Purchase #5 $241.30   11.198%   $268.3208   $268.32   $268.30   $268.30  
  Purchase #6 $23.92   11.201%   $26.5993   $26.60   $26.60   $26.60  
  Purchase #7 $14.32   10.445%   $15.8157   $15.82   $15.80   $15.80  
  7 purchase totals = $933.61       $1,023.6179   $1,023.63   $1,023.60   $1,023.50