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 $108.77   10.595%   $120.2942   $120.29   $120.30   $120.30  
  Purchase #2 $77.99   13.545%   $88.5537   $88.55   $88.55   $88.60  
  Purchase #3 $70.40   5.561%   $74.3149   $74.31   $74.30   $74.30  
  Purchase #4 $243.89   5.760%   $257.9381   $257.94   $257.95   $257.90  
  Purchase #5 $155.48   12.315%   $174.6274   $174.63   $174.65   $174.60  
  Purchase #6 $130.36   3.749%   $135.2472   $135.25   $135.25   $135.20  
  Purchase #7 $98.73   12.732%   $111.3003   $111.30   $111.30   $111.30  
  7 purchase totals = $885.62       $962.2758   $962.27   $962.30   $962.20