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 $54.86   12.364%   $61.6429   $61.64   $61.65   $61.60  
  Purchase #2 $101.75   10.532%   $112.4663   $112.47   $112.45   $112.50  
  Purchase #3 $234.34   7.706%   $252.3982   $252.40   $252.40   $252.40  
  Purchase #4 $226.28   11.460%   $252.2117   $252.21   $252.20   $252.20  
  Purchase #5 $85.93   8.565%   $93.2899   $93.29   $93.30   $93.30  
  Purchase #6 $46.87   6.751%   $50.0342   $50.03   $50.05   $50.00  
  Purchase #7 $138.96   6.418%   $147.8785   $147.88   $147.90   $147.90  
  7 purchase totals = $888.99       $969.9217   $969.92   $969.95   $969.90