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 $246.65   12.412%   $277.2642   $277.26   $277.25   $277.30  
  Purchase #2 $47.41   9.293%   $51.8158   $51.82   $51.80   $51.80  
  Purchase #3 $173.65   10.532%   $191.9388   $191.94   $191.95   $191.90  
  Purchase #4 $203.97   6.835%   $217.9113   $217.91   $217.90   $217.90  
  Purchase #5 $55.36   8.779%   $60.2201   $60.22   $60.20   $60.20  
  Purchase #6 $238.97   4.210%   $249.0306   $249.03   $249.05   $249.00  
  Purchase #7 $113.30   13.308%   $128.378   $128.38   $128.40   $128.40  
  7 purchase totals = $1,079.31       $1,176.5588   $1,176.56   $1,176.55   $1,176.50