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 $245.67   10.792%   $272.1827   $272.18   $272.20   $272.20  
  Purchase #2 $105.63   8.842%   $114.9698   $114.97   $114.95   $115.00  
  Purchase #3 $96.50   4.523%   $100.8647   $100.86   $100.85   $100.90  
  Purchase #4 $159.71   9.243%   $174.472   $174.47   $174.45   $174.50  
  Purchase #5 $147.94   9.446%   $161.9144   $161.91   $161.90   $161.90  
  Purchase #6 $171.94   9.641%   $188.5167   $188.52   $188.50   $188.50  
  Purchase #7 $15.59   5.406%   $16.4328   $16.43   $16.45   $16.40  
  7 purchase totals = $942.98       $1,029.3531   $1,029.34   $1,029.30   $1,029.40