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 $205.58   10.202%   $226.5533   $226.55   $226.55   $226.60  
  Purchase #2 $24.86   10.700%   $27.52   $27.52   $27.50   $27.50  
  Purchase #3 $16.34   10.206%   $18.0077   $18.01   $18.00   $18.00  
  Purchase #4 $72.39   6.622%   $77.1837   $77.18   $77.20   $77.20  
  Purchase #5 $42.38   8.721%   $46.076   $46.08   $46.10   $46.10  
  Purchase #6 $41.76   10.758%   $46.2525   $46.25   $46.25   $46.30  
  Purchase #7 $94.59   9.844%   $103.9014   $103.90   $103.90   $103.90  
  7 purchase totals = $497.90       $545.4946   $545.49   $545.50   $545.60