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 $57.92   6.612%   $61.7497   $61.75   $61.75   $61.70  
  Purchase #2 $180.56   8.133%   $195.2449   $195.24   $195.25   $195.20  
  Purchase #3 $165.41   8.378%   $179.268   $179.27   $179.25   $179.30  
  Purchase #4 $163.96   7.355%   $176.0193   $176.02   $176.00   $176.00  
  Purchase #5 $38.93   6.719%   $41.5457   $41.55   $41.55   $41.50  
  Purchase #6 $130.32   4.852%   $136.6431   $136.64   $136.65   $136.60  
  Purchase #7 $102.72   8.800%   $111.7594   $111.76   $111.75   $111.80  
  7 purchase totals = $839.82       $902.2301   $902.23   $902.20   $902.10