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 $186.41   11.681%   $208.1846   $208.18   $208.20   $208.20  
  Purchase #2 $90.53   6.854%   $96.7349   $96.73   $96.75   $96.70  
  Purchase #3 $215.92   3.504%   $223.4858   $223.49   $223.50   $223.50  
  Purchase #4 $127.27   5.435%   $134.1871   $134.19   $134.20   $134.20  
  Purchase #5 $62.79   5.387%   $66.1725   $66.17   $66.15   $66.20  
  Purchase #6 $77.32   6.416%   $82.2809   $82.28   $82.30   $82.30  
  Purchase #7 $136.87   7.788%   $147.5294   $147.53   $147.55   $147.50  
  7 purchase totals = $897.11       $958.5752   $958.57   $958.65   $958.60