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 $91.66   3.202%   $94.595   $94.60   $94.60   $94.60  
  Purchase #2 $8.78   9.356%   $9.6015   $9.60   $9.60   $9.60  
  Purchase #3 $171.98   12.727%   $193.8679   $193.87   $193.85   $193.90  
  Purchase #4 $182.98   12.606%   $206.0465   $206.05   $206.05   $206.00  
  Purchase #5 $149.49   7.519%   $160.7302   $160.73   $160.75   $160.70  
  Purchase #6 $175.57   9.526%   $192.2948   $192.29   $192.30   $192.30  
  Purchase #7 $236.68   9.203%   $258.4617   $258.46   $258.45   $258.50  
  7 purchase totals = $1,017.14       $1,115.5976   $1,115.60   $1,115.60   $1,115.60