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 $238.95   3.345%   $246.9429   $246.94   $246.95   $246.90  
  Purchase #2 $26.48   13.202%   $29.9759   $29.98   $30.00   $30.00  
  Purchase #3 $96.80   5.201%   $101.8346   $101.83   $101.85   $101.80  
  Purchase #4 $93.71   9.319%   $102.4428   $102.44   $102.45   $102.40  
  Purchase #5 $235.58   11.249%   $262.0804   $262.08   $262.10   $262.10  
  Purchase #6 $132.79   6.427%   $141.3244   $141.32   $141.30   $141.30  
  Purchase #7 $160.47   5.332%   $169.0263   $169.03   $169.05   $169.00  
  7 purchase totals = $984.78       $1,053.6273   $1,053.62   $1,053.70   $1,053.50