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 $167.82   11.371%   $186.9028   $186.90   $186.90   $186.90  
  Purchase #2 $114.38   8.673%   $124.3002   $124.30   $124.30   $124.30  
  Purchase #3 $95.41   8.372%   $103.3977   $103.40   $103.40   $103.40  
  Purchase #4 $45.53   11.305%   $50.6772   $50.68   $50.70   $50.70  
  Purchase #5 $223.80   8.540%   $242.9125   $242.91   $242.90   $242.90  
  Purchase #6 $128.65   7.134%   $137.8279   $137.83   $137.85   $137.80  
  Purchase #7 $167.49   4.597%   $175.1895   $175.19   $175.20   $175.20  
  7 purchase totals = $943.08       $1,021.2078   $1,021.21   $1,021.25   $1,021.20