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 $70.58   8.524%   $76.5962   $76.60   $76.60   $76.60  
  Purchase #2 $224.44   11.554%   $250.3718   $250.37   $250.35   $250.40  
  Purchase #3 $132.99   12.356%   $149.4222   $149.42   $149.40   $149.40  
  Purchase #4 $74.25   3.819%   $77.0856   $77.09   $77.10   $77.10  
  Purchase #5 $237.94   7.133%   $254.9123   $254.91   $254.90   $254.90  
  Purchase #6 $113.61   4.675%   $118.9213   $118.92   $118.90   $118.90  
  Purchase #7 $196.34   5.424%   $206.9895   $206.99   $207.00   $207.00  
  7 purchase totals = $1,050.15       $1,134.2989   $1,134.30   $1,134.25   $1,134.30