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 $76.55   6.233%   $81.3214   $81.32   $81.30   $81.30  
  Purchase #2 $235.63   12.505%   $265.0955   $265.10   $265.10   $265.10  
  Purchase #3 $174.72   10.108%   $192.3807   $192.38   $192.40   $192.40  
  Purchase #4 $48.28   4.464%   $50.4352   $50.44   $50.45   $50.40  
  Purchase #5 $106.91   11.317%   $119.009   $119.01   $119.00   $119.00  
  Purchase #6 $34.66   5.689%   $36.6318   $36.63   $36.65   $36.60  
  Purchase #7 $24.95   12.493%   $28.067   $28.07   $28.05   $28.10  
  7 purchase totals = $701.70       $772.9406   $772.95   $772.95   $772.90