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 $139.61   10.274%   $153.9535   $153.95   $153.95   $154.00  
  Purchase #2 $193.75   12.502%   $217.9726   $217.97   $217.95   $218.00  
  Purchase #3 $235.29   10.578%   $260.179   $260.18   $260.20   $260.20  
  Purchase #4 $74.76   11.471%   $83.3357   $83.34   $83.35   $83.30  
  Purchase #5 $57.45   8.406%   $62.2792   $62.28   $62.30   $62.30  
  Purchase #6 $30.98   5.508%   $32.6864   $32.69   $32.70   $32.70  
  Purchase #7 $218.94   6.737%   $233.69   $233.69   $233.70   $233.70  
  7 purchase totals = $950.78       $1,044.0964   $1,044.10   $1,044.15   $1,044.20