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 $76.37   10.773%   $84.5973   $84.60   $84.60   $84.60  
  Purchase #2 $199.35   13.583%   $226.4277   $226.43   $226.45   $226.40  
  Purchase #3 $120.99   3.465%   $125.1823   $125.18   $125.20   $125.20  
  Purchase #4 $167.25   11.332%   $186.2028   $186.20   $186.20   $186.20  
  Purchase #5 $93.54   3.630%   $96.9355   $96.94   $96.95   $96.90  
  Purchase #6 $164.33   9.153%   $179.3711   $179.37   $179.35   $179.40  
  Purchase #7 $169.93   12.535%   $191.2307   $191.23   $191.25   $191.20  
  7 purchase totals = $991.76       $1,089.9474   $1,089.95   $1,090.00   $1,089.90