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 $59.95   11.186%   $66.656   $66.66   $66.65   $66.70  
  Purchase #2 $200.84   8.456%   $217.823   $217.82   $217.80   $217.80  
  Purchase #3 $224.84   4.487%   $234.9286   $234.93   $234.95   $234.90  
  Purchase #4 $215.48   6.625%   $229.7556   $229.76   $229.75   $229.80  
  Purchase #5 $17.51   10.159%   $19.2888   $19.29   $19.30   $19.30  
  Purchase #6 $150.77   12.765%   $170.0158   $170.02   $170.00   $170.00  
  Purchase #7 $121.64   11.502%   $135.631   $135.63   $135.65   $135.60  
  7 purchase totals = $991.03       $1,074.0988   $1,074.11   $1,074.10   $1,074.10