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 $60.96   7.716%   $65.6637   $65.66   $65.65   $65.70  
  Purchase #2 $196.82   9.238%   $215.0022   $215.00   $215.00   $215.00  
  Purchase #3 $116.81   4.291%   $121.8223   $121.82   $121.80   $121.80  
  Purchase #4 $169.80   5.723%   $179.5177   $179.52   $179.50   $179.50  
  Purchase #5 $78.41   13.680%   $89.1365   $89.14   $89.15   $89.10  
  Purchase #6 $95.61   9.385%   $104.583   $104.58   $104.60   $104.60  
  Purchase #7 $11.38   5.252%   $11.9777   $11.98   $12.00   $12.00  
  7 purchase totals = $729.79       $787.7031   $787.70   $787.70   $787.70