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 $185.77   8.307%   $201.2019   $201.20   $201.20   $201.20  
  Purchase #2 $61.77   7.227%   $66.2341   $66.23   $66.25   $66.20  
  Purchase #3 $147.38   12.435%   $165.7067   $165.71   $165.70   $165.70  
  Purchase #4 $144.70   7.305%   $155.2703   $155.27   $155.25   $155.30  
  Purchase #5 $247.46   3.687%   $256.5839   $256.58   $256.60   $256.60  
  Purchase #6 $162.27   10.208%   $178.8345   $178.83   $178.85   $178.80  
  Purchase #7 $213.64   3.468%   $221.049   $221.05   $221.05   $221.00  
  7 purchase totals = $1,162.99       $1,244.8804   $1,244.87   $1,244.90   $1,244.80