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 $61.87   7.366%   $66.4273   $66.43   $66.45   $66.40  
  Purchase #2 $220.93   11.541%   $246.4275   $246.43   $246.45   $246.40  
  Purchase #3 $89.31   4.113%   $92.9833   $92.98   $93.00   $93.00  
  Purchase #4 $227.51   4.596%   $237.9664   $237.97   $237.95   $238.00  
  Purchase #5 $163.70   13.765%   $186.2333   $186.23   $186.25   $186.20  
  Purchase #6 $23.38   8.339%   $25.3297   $25.33   $25.35   $25.30  
  Purchase #7 $116.71   8.784%   $126.9618   $126.96   $126.95   $127.00  
  7 purchase totals = $903.41       $982.3293   $982.33   $982.40   $982.30