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 $8.62   10.853%   $9.5555   $9.56   $9.55   $9.60  
  Purchase #2 $127.41   11.730%   $142.3552   $142.36   $142.35   $142.40  
  Purchase #3 $172.93   7.619%   $186.1055   $186.11   $186.10   $186.10  
  Purchase #4 $206.67   3.203%   $213.2896   $213.29   $213.30   $213.30  
  Purchase #5 $223.34   3.286%   $230.679   $230.68   $230.70   $230.70  
  Purchase #6 $45.90   12.226%   $51.5117   $51.51   $51.50   $51.50  
  Purchase #7 $166.55   8.474%   $180.6634   $180.66   $180.65   $180.70  
  7 purchase totals = $951.42       $1,014.1599   $1,014.17   $1,014.15   $1,014.30