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 $236.43   11.300%   $263.1466   $263.15   $263.15   $263.10  
  Purchase #2 $230.76   6.424%   $245.584   $245.58   $245.60   $245.60  
  Purchase #3 $24.84   8.358%   $26.9161   $26.92   $26.90   $26.90  
  Purchase #4 $108.69   4.569%   $113.656   $113.66   $113.65   $113.70  
  Purchase #5 $77.26   6.414%   $82.2155   $82.22   $82.20   $82.20  
  Purchase #6 $51.84   13.612%   $58.8965   $58.90   $58.90   $58.90  
  Purchase #7 $208.66   12.350%   $234.4295   $234.43   $234.45   $234.40  
  7 purchase totals = $938.48       $1,024.8442   $1,024.86   $1,024.85   $1,024.80