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 $218.33   8.729%   $237.388   $237.39   $237.40   $237.40  
  Purchase #2 $41.89   12.323%   $47.0521   $47.05   $47.05   $47.10  
  Purchase #3 $158.71   9.312%   $173.4891   $173.49   $173.50   $173.50  
  Purchase #4 $98.49   12.118%   $110.425   $110.43   $110.45   $110.40  
  Purchase #5 $60.80   12.860%   $68.6189   $68.62   $68.60   $68.60  
  Purchase #6 $136.84   11.735%   $152.8982   $152.90   $152.90   $152.90  
  Purchase #7 $60.35   12.820%   $68.0869   $68.09   $68.10   $68.10  
  7 purchase totals = $775.41       $857.9582   $857.97   $858.00   $858.00