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 $24.56   8.266%   $26.5901   $26.59   $26.60   $26.60  
  Purchase #2 $198.56   12.369%   $223.1199   $223.12   $223.10   $223.10  
  Purchase #3 $113.32   8.383%   $122.8196   $122.82   $122.80   $122.80  
  Purchase #4 $86.41   11.308%   $96.1812   $96.18   $96.20   $96.20  
  Purchase #5 $230.68   7.163%   $247.2036   $247.20   $247.20   $247.20  
  Purchase #6 $204.36   10.450%   $225.7156   $225.72   $225.70   $225.70  
  Purchase #7 $244.39   12.636%   $275.2711   $275.27   $275.25   $275.30  
  7 purchase totals = $1,102.28       $1,216.9011   $1,216.90   $1,216.85   $1,216.90