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 $60.63   7.737%   $65.3209   $65.32   $65.30   $65.30  
  Purchase #2 $168.25   3.531%   $174.1909   $174.19   $174.20   $174.20  
  Purchase #3 $144.60   3.556%   $149.742   $149.74   $149.75   $149.70  
  Purchase #4 $215.45   11.378%   $239.9639   $239.96   $239.95   $240.00  
  Purchase #5 $126.93   5.388%   $133.769   $133.77   $133.75   $133.80  
  Purchase #6 $168.82   6.191%   $179.2716   $179.27   $179.25   $179.30  
  Purchase #7 $67.26   11.529%   $75.0144   $75.01   $75.00   $75.00  
  7 purchase totals = $951.94       $1,017.2727   $1,017.26   $1,017.20   $1,017.30