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 $59.56   9.366%   $65.1384   $65.14   $65.15   $65.10  
  Purchase #2 $84.72   4.308%   $88.3697   $88.37   $88.35   $88.40  
  Purchase #3 $103.53   10.358%   $114.2536   $114.25   $114.25   $114.30  
  Purchase #4 $132.49   8.855%   $144.222   $144.22   $144.20   $144.20  
  Purchase #5 $88.26   11.120%   $98.0745   $98.07   $98.05   $98.10  
  Purchase #6 $85.52   9.398%   $93.5572   $93.56   $93.55   $93.60  
  Purchase #7 $182.56   3.444%   $188.8474   $188.85   $188.85   $188.80  
  7 purchase totals = $736.64       $792.4628   $792.46   $792.40   $792.50