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 $65.32   9.312%   $71.4026   $71.40   $71.40   $71.40  
  Purchase #2 $157.64   10.128%   $173.6058   $173.61   $173.60   $173.60  
  Purchase #3 $23.76   5.702%   $25.1148   $25.11   $25.10   $25.10  
  Purchase #4 $211.27   13.402%   $239.5844   $239.58   $239.60   $239.60  
  Purchase #5 $62.63   4.713%   $65.5818   $65.58   $65.60   $65.60  
  Purchase #6 $50.85   11.199%   $56.5447   $56.54   $56.55   $56.50  
  Purchase #7 $203.32   11.853%   $227.4195   $227.42   $227.40   $227.40  
  7 purchase totals = $774.79       $859.2536   $859.24   $859.25   $859.20