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 $58.91   4.573%   $61.604   $61.60   $61.60   $61.60  
  Purchase #2 $43.77   8.332%   $47.4169   $47.42   $47.40   $47.40  
  Purchase #3 $220.73   11.667%   $246.4826   $246.48   $246.50   $246.50  
  Purchase #4 $152.90   13.284%   $173.2112   $173.21   $173.20   $173.20  
  Purchase #5 $37.76   10.205%   $41.6134   $41.61   $41.60   $41.60  
  Purchase #6 $215.43   12.135%   $241.5724   $241.57   $241.55   $241.60  
  Purchase #7 $165.43   10.222%   $182.3403   $182.34   $182.35   $182.30  
  7 purchase totals = $894.93       $994.2408   $994.23   $994.20   $994.20