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 $218.78   7.874%   $236.0067   $236.01   $236.00   $236.00  
  Purchase #2 $104.81   12.291%   $117.6922   $117.69   $117.70   $117.70  
  Purchase #3 $94.58   6.692%   $100.9093   $100.91   $100.90   $100.90  
  Purchase #4 $44.59   5.431%   $47.0117   $47.01   $47.00   $47.00  
  Purchase #5 $160.66   12.450%   $180.6622   $180.66   $180.65   $180.70  
  Purchase #6 $24.66   12.124%   $27.6498   $27.65   $27.65   $27.60  
  Purchase #7 $165.43   12.161%   $185.5479   $185.55   $185.55   $185.50  
  7 purchase totals = $813.51       $895.4798   $895.48   $895.45   $895.40