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 $65.94   4.176%   $68.6937   $68.69   $68.70   $68.70  
  Purchase #2 $119.32   10.851%   $132.2674   $132.27   $132.25   $132.30  
  Purchase #3 $192.33   5.556%   $203.0159   $203.02   $203.00   $203.00  
  Purchase #4 $236.85   11.200%   $263.3772   $263.38   $263.40   $263.40  
  Purchase #5 $61.94   3.623%   $64.1841   $64.18   $64.20   $64.20  
  Purchase #6 $68.46   3.346%   $70.7507   $70.75   $70.75   $70.80  
  Purchase #7 $55.43   11.539%   $61.8261   $61.83   $61.85   $61.80  
  7 purchase totals = $800.27       $864.1151   $864.12   $864.15   $864.20