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 $148.86   11.482%   $165.9521   $165.95   $165.95   $166.00  
  Purchase #2 $234.86   10.686%   $259.9571   $259.96   $259.95   $260.00  
  Purchase #3 $248.85   7.250%   $266.8916   $266.89   $266.90   $266.90  
  Purchase #4 $11.41   7.699%   $12.2885   $12.29   $12.30   $12.30  
  Purchase #5 $146.53   9.511%   $160.4665   $160.47   $160.45   $160.50  
  Purchase #6 $138.85   3.106%   $143.1627   $143.16   $143.15   $143.20  
  Purchase #7 $15.46   7.202%   $16.5734   $16.57   $16.55   $16.60  
  7 purchase totals = $944.82       $1,025.2919   $1,025.29   $1,025.25   $1,025.50