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 $41.77   10.516%   $46.1625   $46.16   $46.15   $46.20  
  Purchase #2 $55.83   12.732%   $62.9383   $62.94   $62.95   $62.90  
  Purchase #3 $101.75   11.536%   $113.4879   $113.49   $113.50   $113.50  
  Purchase #4 $238.42   10.649%   $263.8093   $263.81   $263.80   $263.80  
  Purchase #5 $150.69   11.859%   $168.5603   $168.56   $168.55   $168.60  
  Purchase #6 $90.44   6.135%   $95.9885   $95.99   $96.00   $96.00  
  Purchase #7 $231.74   9.171%   $252.9929   $252.99   $253.00   $253.00  
  7 purchase totals = $910.64       $1,003.9397   $1,003.94   $1,003.95   $1,004.00