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 $16.61   7.564%   $17.8664   $17.87   $17.85   $17.90  
  Purchase #2 $123.46   7.820%   $133.1146   $133.11   $133.10   $133.10  
  Purchase #3 $210.80   9.105%   $229.9933   $229.99   $230.00   $230.00  
  Purchase #4 $153.89   11.326%   $171.3196   $171.32   $171.30   $171.30  
  Purchase #5 $39.62   4.844%   $41.5392   $41.54   $41.55   $41.50  
  Purchase #6 $217.72   10.509%   $240.6002   $240.60   $240.60   $240.60  
  Purchase #7 $210.75   13.740%   $239.7071   $239.71   $239.70   $239.70  
  7 purchase totals = $972.85       $1,074.1404   $1,074.14   $1,074.10   $1,074.10