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 $24.79   7.698%   $26.6983   $26.70   $26.70   $26.70  
  Purchase #2 $174.91   6.155%   $185.6757   $185.68   $185.70   $185.70  
  Purchase #3 $113.39   5.302%   $119.4019   $119.40   $119.40   $119.40  
  Purchase #4 $177.77   13.375%   $201.5467   $201.55   $201.55   $201.50  
  Purchase #5 $182.27   13.349%   $206.6012   $206.60   $206.60   $206.60  
  Purchase #6 $42.48   3.310%   $43.8861   $43.89   $43.90   $43.90  
  Purchase #7 $154.92   5.435%   $163.3399   $163.34   $163.35   $163.30  
  7 purchase totals = $870.53       $947.1498   $947.16   $947.20   $947.10