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 $201.66   4.757%   $211.253   $211.25   $211.25   $211.30  
  Purchase #2 $119.83   10.313%   $132.1881   $132.19   $132.20   $132.20  
  Purchase #3 $245.97   7.446%   $264.2849   $264.28   $264.30   $264.30  
  Purchase #4 $131.48   13.405%   $149.1049   $149.10   $149.10   $149.10  
  Purchase #5 $61.62   7.544%   $66.2686   $66.27   $66.25   $66.30  
  Purchase #6 $122.38   13.589%   $139.0102   $139.01   $139.00   $139.00  
  Purchase #7 $89.47   5.499%   $94.39   $94.39   $94.40   $94.40  
  7 purchase totals = $972.41       $1,056.4997   $1,056.49   $1,056.50   $1,056.60