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 $163.60   11.844%   $182.9768   $182.98   $183.00   $183.00  
  Purchase #2 $108.97   8.355%   $118.0744   $118.07   $118.05   $118.10  
  Purchase #3 $201.43   7.188%   $215.9088   $215.91   $215.90   $215.90  
  Purchase #4 $235.39   10.145%   $259.2703   $259.27   $259.25   $259.30  
  Purchase #5 $68.92   8.699%   $74.9154   $74.92   $74.90   $74.90  
  Purchase #6 $96.53   10.271%   $106.4446   $106.44   $106.45   $106.40  
  Purchase #7 $22.59   8.526%   $24.516   $24.52   $24.50   $24.50  
  7 purchase totals = $897.43       $982.1063   $982.11   $982.05   $982.10