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 $14.69   3.503%   $15.2046   $15.20   $15.20   $15.20  
  Purchase #2 $65.38   8.425%   $70.8883   $70.89   $70.90   $70.90  
  Purchase #3 $196.38   8.313%   $212.7051   $212.71   $212.70   $212.70  
  Purchase #4 $199.64   6.688%   $212.9919   $212.99   $213.00   $213.00  
  Purchase #5 $145.84   5.468%   $153.8145   $153.81   $153.80   $153.80  
  Purchase #6 $232.82   11.682%   $260.018   $260.02   $260.00   $260.00  
  Purchase #7 $141.97   12.371%   $159.5331   $159.53   $159.55   $159.50  
  7 purchase totals = $996.72       $1,085.1555   $1,085.15   $1,085.15   $1,085.10