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 $239.66   11.382%   $266.9381   $266.94   $266.95   $266.90  
  Purchase #2 $228.63   8.836%   $248.8317   $248.83   $248.85   $248.80  
  Purchase #3 $200.56   8.411%   $217.4291   $217.43   $217.45   $217.40  
  Purchase #4 $25.92   6.744%   $27.668   $27.67   $27.65   $27.70  
  Purchase #5 $141.65   6.535%   $150.9068   $150.91   $150.90   $150.90  
  Purchase #6 $116.80   9.600%   $128.0128   $128.01   $128.00   $128.00  
  Purchase #7 $194.49   7.209%   $208.5108   $208.51   $208.50   $208.50  
  7 purchase totals = $1,147.71       $1,248.2973   $1,248.30   $1,248.30   $1,248.20