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 $74.95   13.662%   $85.1897   $85.19   $85.20   $85.20  
  Purchase #2 $153.67   3.484%   $159.0239   $159.02   $159.00   $159.00  
  Purchase #3 $41.60   12.129%   $46.6457   $46.65   $46.65   $46.60  
  Purchase #4 $36.79   5.274%   $38.7303   $38.73   $38.75   $38.70  
  Purchase #5 $239.86   5.423%   $252.8676   $252.87   $252.85   $252.90  
  Purchase #6 $169.69   11.786%   $189.6897   $189.69   $189.70   $189.70  
  Purchase #7 $114.37   7.623%   $123.0884   $123.09   $123.10   $123.10  
  7 purchase totals = $830.93       $895.2353   $895.24   $895.25   $895.20