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 $94.63   3.810%   $98.2354   $98.24   $98.25   $98.20  
  Purchase #2 $223.86   3.786%   $232.3353   $232.34   $232.35   $232.30  
  Purchase #3 $243.26   13.187%   $275.3387   $275.34   $275.35   $275.30  
  Purchase #4 $64.90   5.606%   $68.5383   $68.54   $68.55   $68.50  
  Purchase #5 $8.83   10.195%   $9.7302   $9.73   $9.75   $9.70  
  Purchase #6 $120.94   6.380%   $128.656   $128.66   $128.65   $128.70  
  Purchase #7 $56.47   12.475%   $63.5146   $63.51   $63.50   $63.50  
  7 purchase totals = $812.89       $876.3485   $876.36   $876.40   $876.20