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 $74.46   13.527%   $84.5322   $84.53   $84.55   $84.50  
  Purchase #2 $199.81   12.725%   $225.2358   $225.24   $225.25   $225.20  
  Purchase #3 $150.26   4.537%   $157.0773   $157.08   $157.10   $157.10  
  Purchase #4 $85.36   12.863%   $96.3399   $96.34   $96.35   $96.30  
  Purchase #5 $25.51   8.849%   $27.7674   $27.77   $27.75   $27.80  
  Purchase #6 $223.92   10.199%   $246.7576   $246.76   $246.75   $246.80  
  Purchase #7 $185.87   13.513%   $210.9866   $210.99   $211.00   $211.00  
  7 purchase totals = $945.19       $1,048.6968   $1,048.71   $1,048.75   $1,048.70