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 $213.93   8.295%   $231.6755   $231.68   $231.70   $231.70  
  Purchase #2 $184.53   13.247%   $208.9747   $208.97   $208.95   $209.00  
  Purchase #3 $41.93   9.137%   $45.7611   $45.76   $45.75   $45.80  
  Purchase #4 $30.47   5.168%   $32.0447   $32.04   $32.05   $32.00  
  Purchase #5 $173.47   9.151%   $189.3442   $189.34   $189.35   $189.30  
  Purchase #6 $40.51   12.505%   $45.5758   $45.58   $45.60   $45.60  
  Purchase #7 $223.25   4.394%   $233.0596   $233.06   $233.05   $233.10  
  7 purchase totals = $908.09       $986.4356   $986.43   $986.45   $986.50