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 $239.95   9.534%   $262.8268   $262.83   $262.85   $262.80  
  Purchase #2 $177.55   6.763%   $189.5577   $189.56   $189.55   $189.60  
  Purchase #3 $96.94   11.290%   $107.8845   $107.88   $107.90   $107.90  
  Purchase #4 $182.94   9.632%   $200.5608   $200.56   $200.55   $200.60  
  Purchase #5 $91.29   5.291%   $96.1202   $96.12   $96.10   $96.10  
  Purchase #6 $194.38   12.242%   $218.176   $218.18   $218.20   $218.20  
  Purchase #7 $212.36   13.382%   $240.778   $240.78   $240.80   $240.80  
  7 purchase totals = $1,195.41       $1,315.9040   $1,315.91   $1,315.95   $1,316.00