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 $104.46   9.273%   $114.1466   $114.15   $114.15   $114.10  
  Purchase #2 $30.89   7.415%   $33.1805   $33.18   $33.20   $33.20  
  Purchase #3 $12.84   4.449%   $13.4113   $13.41   $13.40   $13.40  
  Purchase #4 $250.45   6.103%   $265.735   $265.74   $265.75   $265.70  
  Purchase #5 $85.70   9.742%   $94.0489   $94.05   $94.05   $94.00  
  Purchase #6 $161.59   3.842%   $167.7983   $167.80   $167.80   $167.80  
  Purchase #7 $198.62   13.294%   $225.0245   $225.02   $225.00   $225.00  
  7 purchase totals = $844.55       $913.3451   $913.35   $913.35   $913.20