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 $105.95   13.793%   $120.5637   $120.56   $120.55   $120.60  
  Purchase #2 $106.99   11.422%   $119.2104   $119.21   $119.20   $119.20  
  Purchase #3 $164.91   12.731%   $185.9047   $185.90   $185.90   $185.90  
  Purchase #4 $242.27   3.804%   $251.486   $251.49   $251.50   $251.50  
  Purchase #5 $227.81   4.200%   $237.378   $237.38   $237.40   $237.40  
  Purchase #6 $101.52   9.473%   $111.137   $111.14   $111.15   $111.10  
  Purchase #7 $20.98   8.290%   $22.7192   $22.72   $22.70   $22.70  
  7 purchase totals = $970.43       $1,048.3990   $1,048.40   $1,048.40   $1,048.40