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 $156.95   9.395%   $171.6955   $171.70   $171.70   $171.70  
  Purchase #2 $58.96   10.294%   $65.0293   $65.03   $65.05   $65.00  
  Purchase #3 $174.89   8.789%   $190.2611   $190.26   $190.25   $190.30  
  Purchase #4 $8.29   5.507%   $8.7465   $8.75   $8.75   $8.70  
  Purchase #5 $58.51   11.292%   $65.1169   $65.12   $65.10   $65.10  
  Purchase #6 $65.25   3.179%   $67.3243   $67.32   $67.30   $67.30  
  Purchase #7 $159.95   10.694%   $177.0551   $177.06   $177.05   $177.10  
  7 purchase totals = $682.80       $745.2287   $745.24   $745.20   $745.20