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 $61.34   4.294%   $63.9739   $63.97   $63.95   $64.00  
  Purchase #2 $168.32   13.427%   $190.9203   $190.92   $190.90   $190.90  
  Purchase #3 $175.67   4.149%   $182.9585   $182.96   $182.95   $183.00  
  Purchase #4 $93.39   5.667%   $98.6824   $98.68   $98.70   $98.70  
  Purchase #5 $205.80   7.303%   $220.8296   $220.83   $220.85   $220.80  
  Purchase #6 $231.32   4.710%   $242.2152   $242.22   $242.20   $242.20  
  Purchase #7 $46.47   10.432%   $51.3178   $51.32   $51.30   $51.30  
  7 purchase totals = $982.31       $1,050.8977   $1,050.90   $1,050.85   $1,050.90