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 $216.51   4.659%   $226.5972   $226.60   $226.60   $226.60  
  Purchase #2 $164.46   13.599%   $186.8249   $186.82   $186.80   $186.80  
  Purchase #3 $91.45   5.842%   $96.7925   $96.79   $96.80   $96.80  
  Purchase #4 $169.77   9.269%   $185.506   $185.51   $185.50   $185.50  
  Purchase #5 $60.35   11.420%   $67.242   $67.24   $67.25   $67.20  
  Purchase #6 $55.29   3.715%   $57.344   $57.34   $57.35   $57.30  
  Purchase #7 $9.84   11.826%   $11.0037   $11.00   $11.00   $11.00  
  7 purchase totals = $767.67       $831.3103   $831.30   $831.30   $831.20