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 $60.99   6.612%   $65.0227   $65.02   $65.00   $65.00  
  Purchase #2 $156.64   3.206%   $161.6619   $161.66   $161.65   $161.70  
  Purchase #3 $208.41   9.419%   $228.0401   $228.04   $228.05   $228.00  
  Purchase #4 $11.42   10.276%   $12.5935   $12.59   $12.60   $12.60  
  Purchase #5 $63.50   4.406%   $66.2978   $66.30   $66.30   $66.30  
  Purchase #6 $249.51   5.837%   $264.0739   $264.07   $264.05   $264.10  
  Purchase #7 $172.89   3.593%   $179.1019   $179.10   $179.10   $179.10  
  7 purchase totals = $923.36       $976.7918   $976.78   $976.75   $976.80