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 $145.91   11.703%   $162.9858   $162.99   $163.00   $163.00  
  Purchase #2 $144.87   5.339%   $152.6046   $152.60   $152.60   $152.60  
  Purchase #3 $152.57   7.710%   $164.3331   $164.33   $164.35   $164.30  
  Purchase #4 $68.83   4.241%   $71.7491   $71.75   $71.75   $71.70  
  Purchase #5 $231.90   10.538%   $256.3376   $256.34   $256.35   $256.30  
  Purchase #6 $160.85   9.376%   $175.9313   $175.93   $175.95   $175.90  
  Purchase #7 $119.48   6.134%   $126.8089   $126.81   $126.80   $126.80  
  7 purchase totals = $1,024.41       $1,110.7504   $1,110.75   $1,110.80   $1,110.60