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 $239.81   8.539%   $260.2874   $260.29   $260.30   $260.30  
  Purchase #2 $240.97   13.373%   $273.1949   $273.19   $273.20   $273.20  
  Purchase #3 $201.95   11.790%   $225.7599   $225.76   $225.75   $225.80  
  Purchase #4 $171.82   8.785%   $186.9144   $186.91   $186.90   $186.90  
  Purchase #5 $135.86   4.871%   $142.4777   $142.48   $142.50   $142.50  
  Purchase #6 $201.33   12.698%   $226.8949   $226.89   $226.90   $226.90  
  Purchase #7 $126.27   13.228%   $142.973   $142.97   $142.95   $143.00  
  7 purchase totals = $1,318.01       $1,458.5022   $1,458.49   $1,458.50   $1,458.60