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 $84.81   13.567%   $96.3162   $96.32   $96.30   $96.30  
  Purchase #2 $174.56   5.834%   $184.7438   $184.74   $184.75   $184.70  
  Purchase #3 $143.27   11.706%   $160.0412   $160.04   $160.05   $160.00  
  Purchase #4 $34.66   11.795%   $38.7481   $38.75   $38.75   $38.70  
  Purchase #5 $8.41   3.457%   $8.7007   $8.70   $8.70   $8.70  
  Purchase #6 $15.91   12.225%   $17.855   $17.86   $17.85   $17.90  
  Purchase #7 $113.76   4.706%   $119.1135   $119.11   $119.10   $119.10  
  7 purchase totals = $575.38       $625.5185   $625.52   $625.50   $625.40