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 $60.83   10.158%   $67.0091   $67.01   $67.00   $67.00  
  Purchase #2 $15.42   4.115%   $16.0545   $16.05   $16.05   $16.10  
  Purchase #3 $202.28   3.133%   $208.6174   $208.62   $208.60   $208.60  
  Purchase #4 $148.47   8.799%   $161.5339   $161.53   $161.55   $161.50  
  Purchase #5 $22.54   13.691%   $25.626   $25.63   $25.65   $25.60  
  Purchase #6 $218.26   12.786%   $246.1667   $246.17   $246.15   $246.20  
  Purchase #7 $137.81   12.591%   $155.1617   $155.16   $155.15   $155.20  
  7 purchase totals = $805.61       $880.1693   $880.17   $880.15   $880.20