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 $149.85   8.336%   $162.3415   $162.34   $162.35   $162.30  
  Purchase #2 $234.48   6.577%   $249.9017   $249.90   $249.90   $249.90  
  Purchase #3 $224.77   10.326%   $247.9798   $247.98   $248.00   $248.00  
  Purchase #4 $212.87   5.351%   $224.2607   $224.26   $224.25   $224.30  
  Purchase #5 $7.94   7.820%   $8.5609   $8.56   $8.55   $8.60  
  Purchase #6 $72.82   5.640%   $76.927   $76.93   $76.95   $76.90  
  Purchase #7 $60.36   3.301%   $62.3525   $62.35   $62.35   $62.40  
  7 purchase totals = $963.09       $1,032.3241   $1,032.32   $1,032.35   $1,032.40