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 $59.27   11.136%   $65.8703   $65.87   $65.85   $65.90  
  Purchase #2 $246.69   10.820%   $273.3819   $273.38   $273.40   $273.40  
  Purchase #3 $149.74   9.467%   $163.9159   $163.92   $163.90   $163.90  
  Purchase #4 $230.44   10.787%   $255.2976   $255.30   $255.30   $255.30  
  Purchase #5 $17.61   13.697%   $20.022   $20.02   $20.00   $20.00  
  Purchase #6 $178.25   11.811%   $199.3031   $199.30   $199.30   $199.30  
  Purchase #7 $68.34   12.594%   $76.9467   $76.95   $76.95   $76.90  
  7 purchase totals = $950.34       $1,054.7375   $1,054.74   $1,054.70   $1,054.70