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 $164.55   12.848%   $185.6914   $185.69   $185.70   $185.70  
  Purchase #2 $148.32   12.357%   $166.6479   $166.65   $166.65   $166.60  
  Purchase #3 $11.77   12.211%   $13.2072   $13.21   $13.20   $13.20  
  Purchase #4 $118.40   12.435%   $133.123   $133.12   $133.10   $133.10  
  Purchase #5 $150.38   8.785%   $163.5909   $163.59   $163.60   $163.60  
  Purchase #6 $194.58   13.378%   $220.6109   $220.61   $220.60   $220.60  
  Purchase #7 $117.77   11.575%   $131.4019   $131.40   $131.40   $131.40  
  7 purchase totals = $905.77       $1,014.2732   $1,014.27   $1,014.25   $1,014.20