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 $57.68   6.472%   $61.413   $61.41   $61.40   $61.40  
  Purchase #2 $240.53   3.496%   $248.9389   $248.94   $248.95   $248.90  
  Purchase #3 $45.78   11.508%   $51.0484   $51.05   $51.05   $51.00  
  Purchase #4 $42.57   7.873%   $45.9215   $45.92   $45.90   $45.90  
  Purchase #5 $229.28   4.249%   $239.0221   $239.02   $239.00   $239.00  
  Purchase #6 $8.68   7.277%   $9.3116   $9.31   $9.30   $9.30  
  Purchase #7 $106.37   5.522%   $112.2438   $112.24   $112.25   $112.20  
  7 purchase totals = $730.89       $767.8993   $767.89   $767.85   $767.70