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 $234.67   11.649%   $262.0067   $262.01   $262.00   $262.00  
  Purchase #2 $88.37   11.640%   $98.6563   $98.66   $98.65   $98.70  
  Purchase #3 $85.70   4.716%   $89.7416   $89.74   $89.75   $89.70  
  Purchase #4 $164.41   7.305%   $176.4202   $176.42   $176.40   $176.40  
  Purchase #5 $169.72   5.629%   $179.2735   $179.27   $179.25   $179.30  
  Purchase #6 $223.90   12.553%   $252.0062   $252.01   $252.00   $252.00  
  Purchase #7 $11.58   8.408%   $12.5536   $12.55   $12.55   $12.60  
  7 purchase totals = $978.35       $1,070.6581   $1,070.66   $1,070.60   $1,070.70