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 $95.92   11.204%   $106.6669   $106.67   $106.65   $106.70  
  Purchase #2 $63.98   4.405%   $66.7983   $66.80   $66.80   $66.80  
  Purchase #3 $179.30   6.529%   $191.0065   $191.01   $191.00   $191.00  
  Purchase #4 $8.81   10.746%   $9.7567   $9.76   $9.75   $9.80  
  Purchase #5 $121.63   5.203%   $127.9584   $127.96   $127.95   $128.00  
  Purchase #6 $72.85   4.151%   $75.874   $75.87   $75.85   $75.90  
  Purchase #7 $17.29   11.553%   $19.2875   $19.29   $19.30   $19.30  
  7 purchase totals = $559.78       $597.3483   $597.36   $597.30   $597.50