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 $213.66   13.540%   $242.5896   $242.59   $242.60   $242.60  
  Purchase #2 $30.90   6.241%   $32.8285   $32.83   $32.85   $32.80  
  Purchase #3 $157.31   12.463%   $176.9155   $176.92   $176.90   $176.90  
  Purchase #4 $193.37   5.826%   $204.6357   $204.64   $204.65   $204.60  
  Purchase #5 $19.94   13.819%   $22.6955   $22.70   $22.70   $22.70  
  Purchase #6 $44.26   5.833%   $46.8417   $46.84   $46.85   $46.80  
  Purchase #7 $231.53   10.682%   $256.262   $256.26   $256.25   $256.30  
  7 purchase totals = $890.97       $982.7685   $982.78   $982.80   $982.70