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 $216.58   11.389%   $241.2463   $241.25   $241.25   $241.20  
  Purchase #2 $42.96   6.546%   $45.7722   $45.77   $45.75   $45.80  
  Purchase #3 $168.26   4.777%   $176.2978   $176.30   $176.30   $176.30  
  Purchase #4 $175.60   12.454%   $197.4692   $197.47   $197.45   $197.50  
  Purchase #5 $119.66   3.873%   $124.2944   $124.29   $124.30   $124.30  
  Purchase #6 $72.80   4.254%   $75.8969   $75.90   $75.90   $75.90  
  Purchase #7 $118.79   3.199%   $122.5901   $122.59   $122.60   $122.60  
  7 purchase totals = $914.65       $983.5669   $983.57   $983.55   $983.60