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 $213.41   11.563%   $238.0866   $238.09   $238.10   $238.10  
  Purchase #2 $166.69   9.145%   $181.9338   $181.93   $181.95   $181.90  
  Purchase #3 $101.57   11.739%   $113.4933   $113.49   $113.50   $113.50  
  Purchase #4 $173.86   10.419%   $191.9745   $191.97   $191.95   $192.00  
  Purchase #5 $245.71   3.371%   $253.9929   $253.99   $254.00   $254.00  
  Purchase #6 $51.35   10.515%   $56.7495   $56.75   $56.75   $56.70  
  Purchase #7 $7.25   8.608%   $7.8741   $7.87   $7.85   $7.90  
  7 purchase totals = $959.84       $1,044.1047   $1,044.09   $1,044.10   $1,044.10