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 $54.32   11.348%   $60.4842   $60.48   $60.50   $60.50  
  Purchase #2 $86.37   9.521%   $94.5933   $94.59   $94.60   $94.60  
  Purchase #3 $162.42   13.176%   $183.8205   $183.82   $183.80   $183.80  
  Purchase #4 $131.52   6.274%   $139.7716   $139.77   $139.75   $139.80  
  Purchase #5 $15.35   4.210%   $15.9962   $16.00   $16.00   $16.00  
  Purchase #6 $102.29   4.321%   $106.71   $106.71   $106.70   $106.70  
  Purchase #7 $212.93   8.627%   $231.2995   $231.30   $231.30   $231.30  
  7 purchase totals = $765.20       $832.6753   $832.67   $832.65   $832.70