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 $217.70   8.522%   $236.2524   $236.25   $236.25   $236.30  
  Purchase #2 $14.79   10.557%   $16.3514   $16.35   $16.35   $16.40  
  Purchase #3 $151.82   11.142%   $168.7358   $168.74   $168.75   $168.70  
  Purchase #4 $131.36   12.467%   $147.7367   $147.74   $147.75   $147.70  
  Purchase #5 $128.60   11.696%   $143.6411   $143.64   $143.65   $143.60  
  Purchase #6 $239.32   9.549%   $262.1727   $262.17   $262.15   $262.20  
  Purchase #7 $226.85   8.185%   $245.4177   $245.42   $245.40   $245.40  
  7 purchase totals = $1,110.44       $1,220.3078   $1,220.31   $1,220.30   $1,220.30