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 $57.78   8.692%   $62.8022   $62.80   $62.80   $62.80  
  Purchase #2 $226.75   11.120%   $251.9646   $251.96   $251.95   $252.00  
  Purchase #3 $109.36   7.857%   $117.9524   $117.95   $117.95   $118.00  
  Purchase #4 $69.46   9.208%   $75.8559   $75.86   $75.85   $75.90  
  Purchase #5 $46.65   3.357%   $48.216   $48.22   $48.20   $48.20  
  Purchase #6 $87.82   9.639%   $96.285   $96.29   $96.30   $96.30  
  Purchase #7 $246.52   6.513%   $262.5758   $262.58   $262.60   $262.60  
  7 purchase totals = $844.34       $915.6519   $915.66   $915.65   $915.80