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 $214.51   8.510%   $232.7648   $232.76   $232.75   $232.80  
  Purchase #2 $68.99   6.294%   $73.3322   $73.33   $73.35   $73.30  
  Purchase #3 $127.32   12.323%   $143.0096   $143.01   $143.00   $143.00  
  Purchase #4 $32.97   3.673%   $34.181   $34.18   $34.20   $34.20  
  Purchase #5 $99.53   9.141%   $108.628   $108.63   $108.65   $108.60  
  Purchase #6 $216.87   8.633%   $235.5924   $235.59   $235.60   $235.60  
  Purchase #7 $13.63   9.739%   $14.9574   $14.96   $14.95   $15.00  
  7 purchase totals = $773.82       $842.4654   $842.46   $842.50   $842.50