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 $24.67   4.761%   $25.8445   $25.84   $25.85   $25.80  
  Purchase #2 $142.47   5.318%   $150.0466   $150.05   $150.05   $150.00  
  Purchase #3 $185.56   9.324%   $202.8616   $202.86   $202.85   $202.90  
  Purchase #4 $182.91   9.686%   $200.6267   $200.63   $200.65   $200.60  
  Purchase #5 $106.91   4.534%   $111.7573   $111.76   $111.75   $111.80  
  Purchase #6 $86.89   12.731%   $97.952   $97.95   $97.95   $98.00  
  Purchase #7 $64.31   8.475%   $69.7603   $69.76   $69.75   $69.80  
  7 purchase totals = $793.72       $858.8490   $858.85   $858.85   $858.90