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 $11.27   12.327%   $12.6593   $12.66   $12.65   $12.70  
  Purchase #2 $201.51   8.466%   $218.5698   $218.57   $218.55   $218.60  
  Purchase #3 $74.28   3.414%   $76.8159   $76.82   $76.80   $76.80  
  Purchase #4 $190.46   5.147%   $200.263   $200.26   $200.25   $200.30  
  Purchase #5 $13.28   10.133%   $14.6257   $14.63   $14.65   $14.60  
  Purchase #6 $185.75   5.376%   $195.7359   $195.74   $195.75   $195.70  
  Purchase #7 $196.94   4.739%   $206.273   $206.27   $206.25   $206.30  
  7 purchase totals = $873.49       $924.9426   $924.95   $924.90   $925.00