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 $90.56   8.849%   $98.5737   $98.57   $98.55   $98.60  
  Purchase #2 $231.97   8.402%   $251.4601   $251.46   $251.45   $251.50  
  Purchase #3 $15.53   3.562%   $16.0832   $16.08   $16.10   $16.10  
  Purchase #4 $75.40   4.622%   $78.885   $78.89   $78.90   $78.90  
  Purchase #5 $113.97   8.363%   $123.5013   $123.50   $123.50   $123.50  
  Purchase #6 $85.62   7.383%   $91.9413   $91.94   $91.95   $91.90  
  Purchase #7 $133.26   7.126%   $142.7561   $142.76   $142.75   $142.80  
  7 purchase totals = $746.31       $803.2007   $803.20   $803.20   $803.30