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 $58.53   8.557%   $63.5384   $63.54   $63.55   $63.50  
  Purchase #2 $245.25   5.205%   $258.0153   $258.02   $258.00   $258.00  
  Purchase #3 $153.55   5.282%   $161.6605   $161.66   $161.65   $161.70  
  Purchase #4 $53.97   4.187%   $56.2297   $56.23   $56.25   $56.20  
  Purchase #5 $13.96   11.439%   $15.5569   $15.56   $15.55   $15.60  
  Purchase #6 $75.89   8.860%   $82.6139   $82.61   $82.60   $82.60  
  Purchase #7 $241.84   11.621%   $269.9442   $269.94   $269.95   $269.90  
  7 purchase totals = $842.99       $907.5589   $907.56   $907.55   $907.50