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 $247.65   10.567%   $273.8192   $273.82   $273.80   $273.80  
  Purchase #2 $151.48   6.658%   $161.5655   $161.57   $161.55   $161.60  
  Purchase #3 $146.49   11.498%   $163.3334   $163.33   $163.35   $163.30  
  Purchase #4 $215.84   5.782%   $228.3199   $228.32   $228.30   $228.30  
  Purchase #5 $224.91   11.728%   $251.2874   $251.29   $251.30   $251.30  
  Purchase #6 $114.75   10.359%   $126.637   $126.64   $126.65   $126.60  
  Purchase #7 $32.82   8.214%   $35.5158   $35.52   $35.50   $35.50  
  7 purchase totals = $1,133.94       $1,240.4782   $1,240.49   $1,240.45   $1,240.40