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 $212.86   13.471%   $241.5344   $241.53   $241.55   $241.50  
  Purchase #2 $97.66   7.457%   $104.9425   $104.94   $104.95   $104.90  
  Purchase #3 $54.57   3.131%   $56.2786   $56.28   $56.30   $56.30  
  Purchase #4 $142.91   8.402%   $154.9173   $154.92   $154.90   $154.90  
  Purchase #5 $143.29   7.216%   $153.6298   $153.63   $153.65   $153.60  
  Purchase #6 $84.58   12.393%   $95.062   $95.06   $95.05   $95.10  
  Purchase #7 $164.29   10.401%   $181.3778   $181.38   $181.40   $181.40  
  7 purchase totals = $900.16       $987.7424   $987.74   $987.80   $987.70