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 $40.67   10.260%   $44.8427   $44.84   $44.85   $44.80  
  Purchase #2 $72.40   13.203%   $81.959   $81.96   $81.95   $82.00  
  Purchase #3 $128.73   3.632%   $133.4055   $133.41   $133.40   $133.40  
  Purchase #4 $184.68   4.491%   $192.974   $192.97   $192.95   $193.00  
  Purchase #5 $78.25   6.470%   $83.3128   $83.31   $83.30   $83.30  
  Purchase #6 $161.99   6.140%   $171.9362   $171.94   $171.95   $171.90  
  Purchase #7 $232.65   13.404%   $263.8344   $263.83   $263.85   $263.80  
  7 purchase totals = $899.37       $972.2646   $972.26   $972.25   $972.20