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 $65.91   5.758%   $69.7051   $69.71   $69.70   $69.70  
  Purchase #2 $54.88   10.428%   $60.6029   $60.60   $60.60   $60.60  
  Purchase #3 $202.85   6.486%   $216.0069   $216.01   $216.00   $216.00  
  Purchase #4 $6.87   9.672%   $7.5345   $7.53   $7.55   $7.50  
  Purchase #5 $236.63   8.843%   $257.5552   $257.56   $257.55   $257.60  
  Purchase #6 $51.99   8.514%   $56.4164   $56.42   $56.40   $56.40  
  Purchase #7 $80.32   9.311%   $87.7986   $87.80   $87.80   $87.80  
  7 purchase totals = $699.45       $755.6196   $755.63   $755.60   $755.60