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 $59.83   4.166%   $62.3225   $62.32   $62.30   $62.30  
  Purchase #2 $42.74   7.730%   $46.0438   $46.04   $46.05   $46.00  
  Purchase #3 $231.84   7.307%   $248.7805   $248.78   $248.80   $248.80  
  Purchase #4 $57.67   5.442%   $60.8084   $60.81   $60.80   $60.80  
  Purchase #5 $218.74   7.162%   $234.4062   $234.41   $234.40   $234.40  
  Purchase #6 $8.38   9.707%   $9.1934   $9.19   $9.20   $9.20  
  Purchase #7 $77.98   11.496%   $86.9446   $86.94   $86.95   $86.90  
  7 purchase totals = $697.18       $748.4994   $748.49   $748.50   $748.40