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 $69.52   9.658%   $76.2342   $76.23   $76.25   $76.20  
  Purchase #2 $248.39   4.635%   $259.9029   $259.90   $259.90   $259.90  
  Purchase #3 $54.29   3.530%   $56.2064   $56.21   $56.20   $56.20  
  Purchase #4 $115.38   7.649%   $124.2054   $124.21   $124.20   $124.20  
  Purchase #5 $175.49   6.716%   $187.2759   $187.28   $187.30   $187.30  
  Purchase #6 $70.72   9.731%   $77.6018   $77.60   $77.60   $77.60  
  Purchase #7 $71.72   4.305%   $74.8075   $74.81   $74.80   $74.80  
  7 purchase totals = $805.51       $856.2341   $856.24   $856.25   $856.20