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 $208.50   11.273%   $232.0042   $232.00   $232.00   $232.00  
  Purchase #2 $57.89   12.583%   $65.1743   $65.17   $65.15   $65.20  
  Purchase #3 $92.84   3.446%   $96.0393   $96.04   $96.05   $96.00  
  Purchase #4 $66.64   7.525%   $71.6547   $71.65   $71.65   $71.70  
  Purchase #5 $59.66   12.455%   $67.0907   $67.09   $67.10   $67.10  
  Purchase #6 $150.26   10.193%   $165.576   $165.58   $165.60   $165.60  
  Purchase #7 $174.63   8.543%   $189.5486   $189.55   $189.55   $189.50  
  7 purchase totals = $810.42       $887.0878   $887.08   $887.10   $887.10