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 $114.67   3.246%   $118.3922   $118.39   $118.40   $118.40  
  Purchase #2 $50.58   12.597%   $56.9516   $56.95   $56.95   $57.00  
  Purchase #3 $241.29   13.652%   $274.2309   $274.23   $274.25   $274.20  
  Purchase #4 $159.86   4.812%   $167.5525   $167.55   $167.55   $167.60  
  Purchase #5 $227.40   4.107%   $236.7393   $236.74   $236.75   $236.70  
  Purchase #6 $232.52   6.735%   $248.1802   $248.18   $248.20   $248.20  
  Purchase #7 $46.26   7.432%   $49.698   $49.70   $49.70   $49.70  
  7 purchase totals = $1,072.58       $1,151.7447   $1,151.74   $1,151.80   $1,151.80