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 $214.99   12.716%   $242.3281   $242.33   $242.35   $242.30  
  Purchase #2 $33.51   10.141%   $36.9082   $36.91   $36.90   $36.90  
  Purchase #3 $63.98   4.122%   $66.6173   $66.62   $66.60   $66.60  
  Purchase #4 $234.90   3.827%   $243.8896   $243.89   $243.90   $243.90  
  Purchase #5 $98.80   8.763%   $107.4578   $107.46   $107.45   $107.50  
  Purchase #6 $230.60   8.413%   $250.0004   $250.00   $250.00   $250.00  
  Purchase #7 $162.86   13.325%   $184.5611   $184.56   $184.55   $184.60  
  7 purchase totals = $1,039.64       $1,131.7625   $1,131.77   $1,131.75   $1,131.80