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 $116.52   8.633%   $126.5792   $126.58   $126.60   $126.60  
  Purchase #2 $249.63   7.622%   $268.6568   $268.66   $268.65   $268.70  
  Purchase #3 $213.36   5.265%   $224.5934   $224.59   $224.60   $224.60  
  Purchase #4 $84.51   10.254%   $93.1757   $93.18   $93.20   $93.20  
  Purchase #5 $224.41   13.176%   $253.9783   $253.98   $254.00   $254.00  
  Purchase #6 $194.53   9.537%   $213.0823   $213.08   $213.10   $213.10  
  Purchase #7 $43.98   11.282%   $48.9418   $48.94   $48.95   $48.90  
  7 purchase totals = $1,126.94       $1,229.0075   $1,229.01   $1,229.10   $1,229.10