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 $244.61   12.512%   $275.2156   $275.22   $275.20   $275.20  
  Purchase #2 $228.99   4.156%   $238.5068   $238.51   $238.50   $238.50  
  Purchase #3 $63.43   13.453%   $71.9632   $71.96   $71.95   $72.00  
  Purchase #4 $150.64   13.553%   $171.0562   $171.06   $171.05   $171.10  
  Purchase #5 $127.63   9.812%   $140.1531   $140.15   $140.15   $140.20  
  Purchase #6 $146.60   10.372%   $161.8054   $161.81   $161.80   $161.80  
  Purchase #7 $66.59   13.530%   $75.5996   $75.60   $75.60   $75.60  
  7 purchase totals = $1,028.49       $1,134.2999   $1,134.31   $1,134.25   $1,134.40