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 $95.88   10.201%   $105.6607   $105.66   $105.65   $105.70  
  Purchase #2 $169.75   7.644%   $182.7257   $182.73   $182.75   $182.70  
  Purchase #3 $195.31   8.205%   $211.3352   $211.34   $211.35   $211.30  
  Purchase #4 $67.99   7.618%   $73.1695   $73.17   $73.15   $73.20  
  Purchase #5 $109.25   3.742%   $113.3381   $113.34   $113.35   $113.30  
  Purchase #6 $104.27   10.420%   $115.1349   $115.13   $115.15   $115.10  
  Purchase #7 $170.65   6.237%   $181.2934   $181.29   $181.30   $181.30  
  7 purchase totals = $913.10       $982.6575   $982.66   $982.70   $982.60