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 $183.77   10.815%   $203.6447   $203.64   $203.65   $203.60  
  Purchase #2 $177.87   12.419%   $199.9597   $199.96   $199.95   $200.00  
  Purchase #3 $54.39   6.662%   $58.0135   $58.01   $58.00   $58.00  
  Purchase #4 $129.73   3.254%   $133.9514   $133.95   $133.95   $134.00  
  Purchase #5 $169.54   5.276%   $178.4849   $178.48   $178.50   $178.50  
  Purchase #6 $26.90   8.680%   $29.2349   $29.23   $29.25   $29.20  
  Purchase #7 $168.39   6.862%   $179.9449   $179.94   $179.95   $179.90  
  7 purchase totals = $910.59       $983.2340   $983.21   $983.25   $983.20