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 $218.76   9.547%   $239.645   $239.65   $239.65   $239.60  
  Purchase #2 $43.27   11.774%   $48.3646   $48.36   $48.35   $48.40  
  Purchase #3 $60.49   6.282%   $64.29   $64.29   $64.30   $64.30  
  Purchase #4 $25.54   8.478%   $27.7053   $27.71   $27.70   $27.70  
  Purchase #5 $168.43   10.321%   $185.8137   $185.81   $185.80   $185.80  
  Purchase #6 $120.91   4.606%   $126.4791   $126.48   $126.50   $126.50  
  Purchase #7 $11.50   8.404%   $12.4665   $12.47   $12.45   $12.50  
  7 purchase totals = $648.90       $704.7642   $704.77   $704.75   $704.80