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 $185.47   6.504%   $197.533   $197.53   $197.55   $197.50  
  Purchase #2 $31.69   12.618%   $35.6886   $35.69   $35.70   $35.70  
  Purchase #3 $53.37   9.157%   $58.2571   $58.26   $58.25   $58.30  
  Purchase #4 $190.63   8.582%   $206.9899   $206.99   $207.00   $207.00  
  Purchase #5 $237.47   10.748%   $262.9933   $262.99   $263.00   $263.00  
  Purchase #6 $105.59   4.736%   $110.5907   $110.59   $110.60   $110.60  
  Purchase #7 $82.41   7.527%   $88.613   $88.61   $88.60   $88.60  
  7 purchase totals = $886.63       $960.6656   $960.66   $960.70   $960.70