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 $242.29   12.381%   $272.2879   $272.29   $272.30   $272.30  
  Purchase #2 $220.61   6.853%   $235.7284   $235.73   $235.75   $235.70  
  Purchase #3 $219.52   6.451%   $233.6812   $233.68   $233.70   $233.70  
  Purchase #4 $47.91   5.535%   $50.5618   $50.56   $50.55   $50.60  
  Purchase #5 $32.88   8.757%   $35.7593   $35.76   $35.75   $35.80  
  Purchase #6 $84.99   12.327%   $95.4667   $95.47   $95.45   $95.50  
  Purchase #7 $94.86   7.423%   $101.9015   $101.90   $101.90   $101.90  
  7 purchase totals = $943.06       $1,025.3868   $1,025.39   $1,025.40   $1,025.50