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 $221.62   7.658%   $238.5917   $238.59   $238.60   $238.60  
  Purchase #2 $93.67   10.706%   $103.6983   $103.70   $103.70   $103.70  
  Purchase #3 $33.38   10.273%   $36.8091   $36.81   $36.80   $36.80  
  Purchase #4 $117.42   7.234%   $125.9142   $125.91   $125.90   $125.90  
  Purchase #5 $189.58   3.308%   $195.8513   $195.85   $195.85   $195.90  
  Purchase #6 $236.50   13.828%   $269.2032   $269.20   $269.20   $269.20  
  Purchase #7 $236.74   11.364%   $263.6431   $263.64   $263.65   $263.60  
  7 purchase totals = $1,128.91       $1,233.7109   $1,233.70   $1,233.70   $1,233.70