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 $73.76   11.702%   $82.3914   $82.39   $82.40   $82.40  
  Purchase #2 $221.92   9.463%   $242.9203   $242.92   $242.90   $242.90  
  Purchase #3 $49.92   10.206%   $55.0148   $55.01   $55.00   $55.00  
  Purchase #4 $250.35   4.689%   $262.0889   $262.09   $262.10   $262.10  
  Purchase #5 $37.54   11.606%   $41.8969   $41.90   $41.90   $41.90  
  Purchase #6 $32.30   11.423%   $35.9896   $35.99   $36.00   $36.00  
  Purchase #7 $32.67   11.837%   $36.5371   $36.54   $36.55   $36.50  
  7 purchase totals = $698.46       $756.8390   $756.84   $756.85   $756.80