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 $224.73   13.760%   $255.6528   $255.65   $255.65   $255.70  
  Purchase #2 $195.96   6.304%   $208.3133   $208.31   $208.30   $208.30  
  Purchase #3 $45.34   4.657%   $47.4515   $47.45   $47.45   $47.50  
  Purchase #4 $75.29   5.818%   $79.6704   $79.67   $79.65   $79.70  
  Purchase #5 $162.30   3.541%   $168.047   $168.05   $168.05   $168.00  
  Purchase #6 $188.92   5.861%   $199.9926   $199.99   $200.00   $200.00  
  Purchase #7 $220.67   7.457%   $237.1254   $237.13   $237.15   $237.10  
  7 purchase totals = $1,113.21       $1,196.2530   $1,196.25   $1,196.25   $1,196.30