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 $10.98   8.557%   $11.9196   $11.92   $11.90   $11.90  
  Purchase #2 $161.35   5.492%   $170.2113   $170.21   $170.20   $170.20  
  Purchase #3 $73.88   12.863%   $83.3832   $83.38   $83.40   $83.40  
  Purchase #4 $20.52   4.690%   $21.4824   $21.48   $21.50   $21.50  
  Purchase #5 $103.54   8.310%   $112.1442   $112.14   $112.15   $112.10  
  Purchase #6 $202.76   5.529%   $213.9706   $213.97   $213.95   $214.00  
  Purchase #7 $69.97   6.408%   $74.4537   $74.45   $74.45   $74.50  
  7 purchase totals = $643.00       $687.5650   $687.55   $687.55   $687.60