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 $235.43   11.551%   $262.6245   $262.62   $262.60   $262.60  
  Purchase #2 $184.95   8.647%   $200.9426   $200.94   $200.95   $200.90  
  Purchase #3 $34.86   7.646%   $37.5254   $37.53   $37.55   $37.50  
  Purchase #4 $121.89   6.704%   $130.0615   $130.06   $130.05   $130.10  
  Purchase #5 $87.30   12.334%   $98.0676   $98.07   $98.05   $98.10  
  Purchase #6 $115.29   5.821%   $122.001   $122.00   $122.00   $122.00  
  Purchase #7 $57.39   7.584%   $61.7425   $61.74   $61.75   $61.70  
  7 purchase totals = $837.11       $912.9651   $912.96   $912.95   $912.90