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 $208.29   9.397%   $227.863   $227.86   $227.85   $227.90  
  Purchase #2 $82.76   11.106%   $91.9513   $91.95   $91.95   $92.00  
  Purchase #3 $248.76   9.653%   $272.7728   $272.77   $272.75   $272.80  
  Purchase #4 $48.48   11.219%   $53.919   $53.92   $53.90   $53.90  
  Purchase #5 $180.53   9.431%   $197.5558   $197.56   $197.55   $197.60  
  Purchase #6 $226.70   3.510%   $234.6572   $234.66   $234.65   $234.70  
  Purchase #7 $118.52   13.346%   $134.3377   $134.34   $134.35   $134.30  
  7 purchase totals = $1,114.04       $1,213.0568   $1,213.06   $1,213.00   $1,213.20