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 $197.25   13.710%   $224.293   $224.29   $224.30   $224.30  
  Purchase #2 $243.81   11.381%   $271.558   $271.56   $271.55   $271.60  
  Purchase #3 $39.32   3.872%   $40.8425   $40.84   $40.85   $40.80  
  Purchase #4 $186.37   10.664%   $206.2445   $206.24   $206.25   $206.20  
  Purchase #5 $108.28   4.572%   $113.2306   $113.23   $113.25   $113.20  
  Purchase #6 $25.93   12.632%   $29.2055   $29.21   $29.20   $29.20  
  Purchase #7 $123.44   12.862%   $139.3169   $139.32   $139.30   $139.30  
  7 purchase totals = $924.40       $1,024.6910   $1,024.69   $1,024.70   $1,024.60