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 $69.45   12.233%   $77.9458   $77.95   $77.95   $77.90  
  Purchase #2 $44.73   12.323%   $50.2421   $50.24   $50.25   $50.20  
  Purchase #3 $156.45   12.157%   $175.4696   $175.47   $175.45   $175.50  
  Purchase #4 $53.27   8.204%   $57.6403   $57.64   $57.65   $57.60  
  Purchase #5 $99.53   12.524%   $111.9951   $112.00   $112.00   $112.00  
  Purchase #6 $245.93   11.158%   $273.3709   $273.37   $273.35   $273.40  
  Purchase #7 $239.51   6.509%   $255.0997   $255.10   $255.10   $255.10  
  7 purchase totals = $908.87       $1,001.7635   $1,001.77   $1,001.75   $1,001.70