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 $132.78   12.634%   $149.5554   $149.56   $149.55   $149.60  
  Purchase #2 $231.97   7.428%   $249.2007   $249.20   $249.20   $249.20  
  Purchase #3 $94.88   12.308%   $106.5578   $106.56   $106.55   $106.60  
  Purchase #4 $61.40   11.693%   $68.5795   $68.58   $68.60   $68.60  
  Purchase #5 $239.78   5.198%   $252.2438   $252.24   $252.25   $252.20  
  Purchase #6 $36.54   5.851%   $38.678   $38.68   $38.70   $38.70  
  Purchase #7 $88.99   10.572%   $98.398   $98.40   $98.40   $98.40  
  7 purchase totals = $886.34       $963.2132   $963.22   $963.25   $963.30