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 $211.57   11.818%   $236.5733   $236.57   $236.55   $236.60  
  Purchase #2 $104.62   12.528%   $117.7268   $117.73   $117.75   $117.70  
  Purchase #3 $64.50   9.190%   $70.4276   $70.43   $70.45   $70.40  
  Purchase #4 $231.93   13.103%   $262.3198   $262.32   $262.30   $262.30  
  Purchase #5 $192.54   8.280%   $208.4823   $208.48   $208.50   $208.50  
  Purchase #6 $54.84   4.406%   $57.2563   $57.26   $57.25   $57.30  
  Purchase #7 $204.43   13.505%   $232.0383   $232.04   $232.05   $232.00  
  7 purchase totals = $1,064.43       $1,184.8244   $1,184.83   $1,184.85   $1,184.80