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 $49.49   4.834%   $51.8823   $51.88   $51.90   $51.90  
  Purchase #2 $113.87   3.694%   $118.0764   $118.08   $118.10   $118.10  
  Purchase #3 $58.88   4.631%   $61.6067   $61.61   $61.60   $61.60  
  Purchase #4 $97.54   7.370%   $104.7287   $104.73   $104.75   $104.70  
  Purchase #5 $200.44   7.742%   $215.9581   $215.96   $215.95   $216.00  
  Purchase #6 $23.64   10.603%   $26.1465   $26.15   $26.15   $26.10  
  Purchase #7 $180.27   4.238%   $187.9098   $187.91   $187.90   $187.90  
  7 purchase totals = $724.13       $766.3085   $766.32   $766.35   $766.30