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 $126.85   5.844%   $134.2631   $134.26   $134.25   $134.30  
  Purchase #2 $51.77   5.522%   $54.6287   $54.63   $54.65   $54.60  
  Purchase #3 $238.80   3.245%   $246.5491   $246.55   $246.55   $246.50  
  Purchase #4 $140.30   11.856%   $156.934   $156.93   $156.95   $156.90  
  Purchase #5 $99.86   5.629%   $105.4811   $105.48   $105.50   $105.50  
  Purchase #6 $170.46   9.357%   $186.4099   $186.41   $186.40   $186.40  
  Purchase #7 $77.85   8.221%   $84.25   $84.25   $84.25   $84.30  
  7 purchase totals = $905.89       $968.5159   $968.51   $968.55   $968.50