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 $57.84   8.796%   $62.9276   $62.93   $62.95   $62.90  
  Purchase #2 $106.70   10.853%   $118.2802   $118.28   $118.30   $118.30  
  Purchase #3 $18.88   8.137%   $20.4163   $20.42   $20.40   $20.40  
  Purchase #4 $174.80   4.554%   $182.7604   $182.76   $182.75   $182.80  
  Purchase #5 $177.66   10.314%   $195.9839   $195.98   $196.00   $196.00  
  Purchase #6 $146.47   9.839%   $160.8812   $160.88   $160.90   $160.90  
  Purchase #7 $117.41   7.827%   $126.5997   $126.60   $126.60   $126.60  
  7 purchase totals = $799.76       $867.8493   $867.85   $867.90   $867.90