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 $226.77   3.108%   $233.818   $233.82   $233.80   $233.80  
  Purchase #2 $26.71   13.402%   $30.2897   $30.29   $30.30   $30.30  
  Purchase #3 $211.52   12.129%   $237.1753   $237.18   $237.20   $237.20  
  Purchase #4 $73.73   7.667%   $79.3829   $79.38   $79.40   $79.40  
  Purchase #5 $248.83   10.825%   $275.7658   $275.77   $275.75   $275.80  
  Purchase #6 $197.94   11.548%   $220.7981   $220.80   $220.80   $220.80  
  Purchase #7 $228.72   9.518%   $250.4896   $250.49   $250.50   $250.50  
  7 purchase totals = $1,214.22       $1,327.7194   $1,327.73   $1,327.75   $1,327.80