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 $82.61   13.801%   $94.011   $94.01   $94.00   $94.00  
  Purchase #2 $50.81   13.170%   $57.5017   $57.50   $57.50   $57.50  
  Purchase #3 $24.46   7.711%   $26.3461   $26.35   $26.35   $26.30  
  Purchase #4 $220.57   3.431%   $228.1378   $228.14   $228.15   $228.10  
  Purchase #5 $195.60   6.684%   $208.6739   $208.67   $208.65   $208.70  
  Purchase #6 $61.82   6.855%   $66.0578   $66.06   $66.05   $66.10  
  Purchase #7 $201.77   4.561%   $210.9727   $210.97   $210.95   $211.00  
  7 purchase totals = $837.64       $891.7010   $891.70   $891.65   $891.70