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 $68.49   12.813%   $77.2656   $77.27   $77.25   $77.30  
  Purchase #2 $214.73   11.687%   $239.8255   $239.83   $239.85   $239.80  
  Purchase #3 $41.37   13.306%   $46.8747   $46.87   $46.85   $46.90  
  Purchase #4 $220.35   12.379%   $247.6271   $247.63   $247.65   $247.60  
  Purchase #5 $85.27   13.704%   $96.9554   $96.96   $96.95   $97.00  
  Purchase #6 $204.59   4.634%   $214.0707   $214.07   $214.05   $214.10  
  Purchase #7 $38.67   8.208%   $41.844   $41.84   $41.85   $41.80  
  7 purchase totals = $873.47       $964.4630   $964.47   $964.45   $964.50