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 $82.56   6.603%   $88.0114   $88.01   $88.00   $88.00  
  Purchase #2 $133.58   13.749%   $151.9459   $151.95   $151.95   $151.90  
  Purchase #3 $208.51   4.734%   $218.3809   $218.38   $218.40   $218.40  
  Purchase #4 $245.71   10.111%   $270.5537   $270.55   $270.55   $270.60  
  Purchase #5 $56.54   3.514%   $58.5268   $58.53   $58.55   $58.50  
  Purchase #6 $177.85   8.727%   $193.371   $193.37   $193.35   $193.40  
  Purchase #7 $142.76   12.820%   $161.0618   $161.06   $161.05   $161.10  
  7 purchase totals = $1,047.51       $1,141.8515   $1,141.85   $1,141.85   $1,141.90