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 $59.81   13.147%   $67.6732   $67.67   $67.65   $67.70  
  Purchase #2 $144.42   12.268%   $162.1374   $162.14   $162.15   $162.10  
  Purchase #3 $155.49   7.605%   $167.315   $167.32   $167.30   $167.30  
  Purchase #4 $21.25   10.102%   $23.3967   $23.40   $23.40   $23.40  
  Purchase #5 $154.74   12.404%   $173.9339   $173.93   $173.95   $173.90  
  Purchase #6 $197.96   9.653%   $217.0691   $217.07   $217.05   $217.10  
  Purchase #7 $217.47   8.452%   $235.8506   $235.85   $235.85   $235.90  
  7 purchase totals = $951.14       $1,047.3759   $1,047.38   $1,047.35   $1,047.40