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 $27.60   5.401%   $29.0907   $29.09   $29.10   $29.10  
  Purchase #2 $5.74   6.200%   $6.0959   $6.10   $6.10   $6.10  
  Purchase #3 $149.33   9.368%   $163.3192   $163.32   $163.30   $163.30  
  Purchase #4 $170.40   9.680%   $186.8947   $186.89   $186.90   $186.90  
  Purchase #5 $243.38   5.202%   $256.0406   $256.04   $256.05   $256.00  
  Purchase #6 $13.66   12.607%   $15.3821   $15.38   $15.40   $15.40  
  Purchase #7 $190.99   8.272%   $206.7887   $206.79   $206.80   $206.80  
  7 purchase totals = $801.10       $863.6119   $863.61   $863.65   $863.60